The figure shows how to couple two TTL circuits using an optical coupler to obtain isolation. The circuit is shown in the August 1992 issue of Radio Electronics magazine.
We find this microphone voice effect in 1992 documentation. The vibration of the relay contacts...
We can also use the 4011 on this CMOS circuit that makes use of a crystal headset. The power...
We found this circuit in documentation from the 1980s. The integrated circuit used is uncommon today,...